<?// This will not work as expected on Linux.ob_implicit_flush (1);for($i=0;$i<10;$i++) { echo "grrrrrrrrrr\n";sleep(1);}?>

This feature happens on Linux versions of PHP, in all versions of php4 prior to 4.3.3 (don't know yet for the next ones) but also in php5 beta1. ob_implicit_flush has NO EFFECT on command-line (console, CLI) scripts, no flushing at all will be made, all output will be sent at the end of the script.

From experimenting, it looks like using sessions with session.use_trans_sid=1 will force your output to be buffered regardless of this setting.

My guess is that this is so PHP can hunt for URLs in your output to automatically add the Session ID to them. It must wait until script output is complete before it starts that replacement, rather than doing it "on the fly".

When i comment out my session_start() line, i get continuous output to the browser. Put it back in, and i only see the page when it's completely loaded. Change session.use_trans_sid = 0 and i get continuous output again.

Note that the name ob_implicit_flush is misleading. Despite its name, this function does NOT work with the user output buffer, i.e. the one that the rest of the ob_* functions work with. It will NOT do an automatic ob_flush(). It will do an automatic flush(). Different things.

This will output as it goes. This is only a problem if you only want one part of the output to come out in real time, and want the rest buffered. In that case, since there's no function to do an implicit ob_flush() every time, you need to call it explicitly. For example, this works:

<?php ob_start(); // not needed if output_buffering is on in php.iniob_implicit_flush(); // implicitly calls flush() after every ob_flush()

echo "This output is buffered.\n"; echo "As is this.\n";

for ($i = 0; $i < 10; $i++) { echo "$i\n";ob_flush();sleep(1); }?>

Note also that some browsers may wait until they have a certain amount of output. See flush [ http://php.net/manual/en/function.flush.php ] for details. It was my case with Firefox (Iceweasel 17.0); unless I output 1024 bytes at the beginning, it does not begin to output.